Some commentary..
Technically, a larger pack pack is (quite a lot) more efficient, and will last much longer and provide much more power overall, due to much lower C rates.
This is very much the reality, as well as the theory.
e:
6 batteries in parallel, running one at a time, for a useful power-output to 50% dod, in one hour.
The 6 batteries will provide x power, say 3 knots on some particular theoretical craft, or 3 knots/hr, 18 miles total.
If in parallel, You will likely get about 9 hours to 50% dod, and the battery lifetime will be 50% longer, over the useful life of the batteries.
Or 27 miles range, vs 18, 50% more.
More or less, it is an example of how it works..
But..
1.
IF for some reason You bust the pack, due to overcharging, undercharging, or overusing, the whole thing is toast vs just one battery.
2.
IF for some reason You run out of juice, You have no options.
BUT You are probably very much less likely to run out of juice with 27 miles, vs 18.
You get 50% more useful life with 6xP, but must then make sure that it is sufficient.
This is not much different to exhausting 6 batteries one after the other, and then being out of juice, but with only half the total capacity.
A good way to think about all this is;
1.
double the voltage, twice, for about 20-25% increase in range/performance/results.
So, vs a 12 V system,
12V x 2 x 2 = 48 V.
A 48 volt system will be about 25% more efficient, due to lower losses in cables, inductance, back emf, etc.
Often more, in marine stuff, details matter a lot..
2.
Triple the capacity, for 20-25% increase in range/efficiency/total power; depending on what You need (a bit less benefit in lion batteries).
So, if 1 kWh of batteries provide say 10 miles at 2 knots,
3 kWh will typically provide == 3 x 1 x 1.25 = 3.6 miles.
3.
Double the prop D for a great increase in efficiency.
Often 30-50%, upto 100%.
But it is hard to do, needs different pitches, etc.. and is very seldom if almost-never done.
The best part about electric drive, is that You *could* increase the prop size, lower pitch, and still get great results, because electric drives are happy to run slow, with full torque and power, without loss of efficiency.
My thinking was that connected in parallel, it would reduce DOD, keeping them more in balance and possibly extending life. Maybe that is not worth it?
-- -hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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